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//! Precedence representation.
use crate::{
ast::{self, BinaryOp, Expr, HasArgList},
match_ast, AstNode, SyntaxNode,
};
impl Expr {
// Implementation is based on
// - https://doc.rust-lang.org/reference/expressions.html#expression-precedence
// - https://matklad.github.io/2020/04/13/simple-but-powerful-pratt-parsing.html
// - rustc source, including, but not limited to
// - https://github.com/rust-lang/rust/blob/b6852428a8ea9728369b64b9964cad8e258403d3/compiler/rustc_ast/src/util/parser.rs#L296
/// Returns `true` if `self` would need to be wrapped in parentheses given that its parent is `parent`.
pub fn needs_parens_in(&self, parent: SyntaxNode) -> bool {
match_ast! {
match parent {
ast::Expr(e) => self.needs_parens_in_expr(&e),
ast::Stmt(e) => self.needs_parens_in_stmt(Some(&e)),
ast::StmtList(_) => self.needs_parens_in_stmt(None),
ast::ArgList(_) => false,
ast::MatchArm(_) => false,
_ => false,
}
}
}
fn needs_parens_in_expr(&self, parent: &Expr) -> bool {
// Special-case block weirdness
if parent.child_is_followed_by_a_block() {
use Expr::*;
match self {
// Cases like `if return {}` (need parens or else `{}` is returned, instead of being `if`'s body)
ReturnExpr(e) if e.expr().is_none() => return true,
BreakExpr(e) if e.expr().is_none() => return true,
YieldExpr(e) if e.expr().is_none() => return true,
// Same but with `..{}`
RangeExpr(e) if matches!(e.end(), Some(BlockExpr(..))) => return true,
// Similarly with struct literals, e.g. `if S{} == 1 {}`
_ if self.contains_exterior_struct_lit() => return true,
_ => {}
}
}
// Special-case `return.f()`
if self.is_ret_like_with_no_value() && parent.is_postfix() {
return false;
}
if self.is_paren_like()
|| parent.is_paren_like()
|| self.is_prefix() && (parent.is_prefix() || !self.is_ordered_before(parent))
|| self.is_postfix() && (parent.is_postfix() || self.is_ordered_before(parent))
{
return false;
}
let (left, right, inv) = match self.is_ordered_before(parent) {
true => (self, parent, false),
false => (parent, self, true),
};
let (_, left_right_bp) = left.binding_power();
let (right_left_bp, _) = right.binding_power();
(left_right_bp < right_left_bp) ^ inv
}
fn needs_parens_in_stmt(&self, stmt: Option<&ast::Stmt>) -> bool {
use Expr::*;
// Prevent false-positives in cases like `fn x() -> u8 { ({ 0 } + 1) }`,
// `{ { 0 } + 1 }` won't parse -- `{ 0 }` would be parsed as a self-contained stmt,
// leaving `+ 1` as a parse error.
let mut innermost = self.clone();
loop {
let next = match &innermost {
BinExpr(e) => e.lhs(),
CallExpr(e) => e.expr(),
CastExpr(e) => e.expr(),
IndexExpr(e) => e.base(),
_ => break,
};
if let Some(next) = next {
innermost = next;
if !innermost.requires_semi_to_be_stmt() {
return true;
}
} else {
break;
}
}
// Not every expression can be followed by `else` in the `let-else`
if let Some(ast::Stmt::LetStmt(e)) = stmt {
if e.let_else().is_some() {
match self {
BinExpr(e)
if e.op_kind()
.map(|op| matches!(op, BinaryOp::LogicOp(_)))
.unwrap_or(false) =>
{
return true
}
_ if self.clone().trailing_brace().is_some() => return true,
_ => {}
}
}
}
false
}
/// Returns left and right so-called "binding powers" of this expression.
fn binding_power(&self) -> (u8, u8) {
use ast::{ArithOp::*, BinaryOp::*, Expr::*, LogicOp::*};
match self {
// (0, 0) -- paren-like/nullary
// (0, N) -- prefix
// (N, 0) -- postfix
// (N, N) -- infix, requires parens
// (N, N+1) -- infix, left to right associative
// (N+1, N) -- infix, right to left associative
// N is odd
//
ContinueExpr(_) => (0, 0),
ClosureExpr(_) | ReturnExpr(_) | YieldExpr(_) | YeetExpr(_) | BreakExpr(_) => (0, 1),
RangeExpr(_) => (5, 5),
BinExpr(e) => {
// Return a dummy value if we don't know the op
let Some(op) = e.op_kind() else { return (0, 0) };
match op {
Assignment { .. } => (4, 3),
//
// Ranges are here in order :)
//
LogicOp(op) => match op {
Or => (7, 8),
And => (9, 10),
},
CmpOp(_) => (11, 11),
ArithOp(op) => match op {
BitOr => (13, 14),
BitXor => (15, 16),
BitAnd => (17, 18),
Shl | Shr => (19, 20),
Add | Sub => (21, 22),
Mul | Div | Rem => (23, 24),
},
}
}
CastExpr(_) => (25, 26),
BoxExpr(_) | RefExpr(_) | LetExpr(_) | PrefixExpr(_) => (0, 27),
AwaitExpr(_) | CallExpr(_) | MethodCallExpr(_) | IndexExpr(_) | TryExpr(_)
| MacroExpr(_) => (29, 0),
FieldExpr(_) => (31, 32),
ArrayExpr(_) | TupleExpr(_) | Literal(_) | PathExpr(_) | ParenExpr(_) | IfExpr(_)
| WhileExpr(_) | ForExpr(_) | LoopExpr(_) | MatchExpr(_) | BlockExpr(_)
| RecordExpr(_) | UnderscoreExpr(_) => (0, 0),
}
}
fn is_paren_like(&self) -> bool {
matches!(self.binding_power(), (0, 0))
}
fn is_prefix(&self) -> bool {
matches!(self.binding_power(), (0, 1..))
}
fn is_postfix(&self) -> bool {
matches!(self.binding_power(), (1.., 0))
}
/// Returns `true` if this expression can't be a standalone statement.
fn requires_semi_to_be_stmt(&self) -> bool {
use Expr::*;
!matches!(
self,
IfExpr(..) | MatchExpr(..) | BlockExpr(..) | WhileExpr(..) | LoopExpr(..) | ForExpr(..)
)
}
/// If an expression ends with `}`, returns the innermost expression ending in this `}`.
fn trailing_brace(mut self) -> Option<Expr> {
use Expr::*;
loop {
let rhs = match self {
RefExpr(e) => e.expr(),
BinExpr(e) => e.rhs(),
BoxExpr(e) => e.expr(),
BreakExpr(e) => e.expr(),
LetExpr(e) => e.expr(),
RangeExpr(e) => e.end(),
ReturnExpr(e) => e.expr(),
PrefixExpr(e) => e.expr(),
YieldExpr(e) => e.expr(),
ClosureExpr(e) => e.body(),
BlockExpr(..) | ForExpr(..) | IfExpr(..) | LoopExpr(..) | MatchExpr(..)
| RecordExpr(..) | WhileExpr(..) => break Some(self),
_ => break None,
};
self = rhs?;
}
}
/// Expressions that syntactically contain an "exterior" struct literal i.e., not surrounded by any
/// parens or other delimiters, e.g., `X { y: 1 }`, `X { y: 1 }.method()`, `foo == X { y: 1 }` and
/// `X { y: 1 } == foo` all do, but `(X { y: 1 }) == foo` does not.
fn contains_exterior_struct_lit(&self) -> bool {
return contains_exterior_struct_lit_inner(self).is_some();
fn contains_exterior_struct_lit_inner(expr: &Expr) -> Option<()> {
use Expr::*;
match expr {
RecordExpr(..) => Some(()),
// X { y: 1 } + X { y: 2 }
BinExpr(e) => e
.lhs()
.as_ref()
.and_then(contains_exterior_struct_lit_inner)
.or_else(|| e.rhs().as_ref().and_then(contains_exterior_struct_lit_inner)),
// `&X { y: 1 }`, `X { y: 1 }.y`, `X { y: 1 }.bar(...)`, etc
IndexExpr(e) => contains_exterior_struct_lit_inner(&e.base()?),
AwaitExpr(e) => contains_exterior_struct_lit_inner(&e.expr()?),
PrefixExpr(e) => contains_exterior_struct_lit_inner(&e.expr()?),
CastExpr(e) => contains_exterior_struct_lit_inner(&e.expr()?),
FieldExpr(e) => contains_exterior_struct_lit_inner(&e.expr()?),
MethodCallExpr(e) => contains_exterior_struct_lit_inner(&e.receiver()?),
_ => None,
}
}
}
/// Returns true if self is one of `return`, `break`, `continue` or `yield` with **no associated value**.
fn is_ret_like_with_no_value(&self) -> bool {
use Expr::*;
match self {
ReturnExpr(e) => e.expr().is_none(),
BreakExpr(e) => e.expr().is_none(),
ContinueExpr(_) => true,
YieldExpr(e) => e.expr().is_none(),
_ => false,
}
}
fn is_ordered_before(&self, other: &Expr) -> bool {
use Expr::*;
return order(self) < order(other);
/// Returns text range that can be used to compare two expression for order (which goes first).
fn order(this: &Expr) -> rowan::TextSize {
// For non-paren-like operators: get the operator itself
let token = match this {
RangeExpr(e) => e.op_token(),
BinExpr(e) => e.op_token(),
CastExpr(e) => e.as_token(),
FieldExpr(e) => e.dot_token(),
AwaitExpr(e) => e.dot_token(),
BoxExpr(e) => e.box_token(),
BreakExpr(e) => e.break_token(),
CallExpr(e) => e.arg_list().and_then(|args| args.l_paren_token()),
ClosureExpr(e) => e.param_list().and_then(|params| params.l_paren_token()),
ContinueExpr(e) => e.continue_token(),
IndexExpr(e) => e.l_brack_token(),
MethodCallExpr(e) => e.dot_token(),
PrefixExpr(e) => e.op_token(),
RefExpr(e) => e.amp_token(),
ReturnExpr(e) => e.return_token(),
TryExpr(e) => e.question_mark_token(),
YieldExpr(e) => e.yield_token(),
YeetExpr(e) => e.do_token(),
LetExpr(e) => e.let_token(),
ArrayExpr(_) | TupleExpr(_) | Literal(_) | PathExpr(_) | ParenExpr(_)
| IfExpr(_) | WhileExpr(_) | ForExpr(_) | LoopExpr(_) | MatchExpr(_)
| BlockExpr(_) | RecordExpr(_) | UnderscoreExpr(_) | MacroExpr(_) => None,
};
token.map(|t| t.text_range()).unwrap_or_else(|| this.syntax().text_range()).start()
}
}
fn child_is_followed_by_a_block(&self) -> bool {
use Expr::*;
match self {
ArrayExpr(_) | AwaitExpr(_) | BlockExpr(_) | CallExpr(_) | CastExpr(_)
| ClosureExpr(_) | FieldExpr(_) | IndexExpr(_) | Literal(_) | LoopExpr(_)
| MacroExpr(_) | MethodCallExpr(_) | ParenExpr(_) | PathExpr(_) | RecordExpr(_)
| TryExpr(_) | TupleExpr(_) | UnderscoreExpr(_) => false,
// For BinExpr and RangeExpr this is technically wrong -- the child can be on the left...
BinExpr(_) | RangeExpr(_) | BoxExpr(_) | BreakExpr(_) | ContinueExpr(_)
| PrefixExpr(_) | RefExpr(_) | ReturnExpr(_) | YieldExpr(_) | YeetExpr(_)
| LetExpr(_) => self
.syntax()
.parent()
.and_then(Expr::cast)
.map(|e| e.child_is_followed_by_a_block())
.unwrap_or(false),
ForExpr(_) | IfExpr(_) | MatchExpr(_) | WhileExpr(_) => true,
}
}
}